var mergeTwoLists = function (l1, l2) {
    if (l1 == null || l2 == null) {
        return l1==null?l2:l1
    }
    let head = l1.val > l2.val ? l2 : l1
    var tmp = head;
    while (l1 && l2) {
        
    }
    return head
}
var l1 = {
    val: 5,
    next: null
}
var l2 = {
    val: 1,
    next: {
        val: 2,
        next: {
            val: 4,
            next: null
        }
    }
}

console.log(mergeTwoLists(l1, l2))